1. Field of the Invention
The present invention relates in general to air conditioning systems of heat pump type for motor vehicles, particularly for electric vehicles, and more particularly, the present invention relates to the heat pump type air conditioning systems having a refrigerating cycle. More specifically, the present invention is concerned with the heat pump type air heating systems which can instantly heat air in the passenger room after start-up thereof and can effectively dehumidify the heated air in the passenger room.
2. Description of the Prior Art
In order to heat air in the passenger room of electric vehicles, heat pump systems are commonly used, which collect outside heat for the heating. One of such heat pump systems is shown in FIG. 18 of the accompanying drawings, which is designated by numeral 100.
As shown in the drawing, the heat pump system 100 has an evaporator 101 which is positioned outside the passenger room to collect outside heat by using a coolant which has been vaporized at a temperature lower than the outside temperature. The coolant thus accumulating heat therein is compressed by a compressor 103 and led to a condenser 105, which is located in a duct 113, to radiate the heat to air in the duct 113. The heated air is led to desired positions of the passenger room with an aid of an electric blower 115 installed in the duct 113. Designated by numerals 107 and 109 are an expansion valve and a receiver dryer (viz., liquid tank) respectively. The receiver dryer 109 has two functions, one being to separate gaseous coolant from liquid coolant, and the other being to dry the coolant.
However, the heat pump system 100 has no function to dehumidify the heated air fed to the passenger room. Thus, in winter, the operation of the system 100 tends to induce undesired misting on a windshield caused by moisture in the passenger room, which prevents the driver from driving safely.
To solve such drawback, another heat pump system 110 has been proposed by Japanese Patent First Provisional Publication 5-201243, which is shown in FIG. 19 of the accompanying drawings.
As shown in the drawing, in the system 110, there are further employed another (or inside) evaporator 117 which is installed in the duct 113 upstream of the condenser 105, a bypass passage 112 which bypasses the outside evaporator 101, a two-way valve 111 which selectively connects the compressor 103 with the outside evaporator 101 or the bypass passage 112, and a check valve 119 which is arranged between the outside evaporator 101 and the bypass passage 112 as shown.
When dehumidification of air in the passenger room is needed, the two-way valve 111 takes the illustrated position. Under this condition, the coolant is forced to flow in the direction of the arrows. With this, the air from the electric blower 115 is cooled and thus dehumidified by the inside evaporator 117 and then heated by the condenser 105 before entering the passenger room.
However, even the heat pump system 110 has failed to obtain a satisfied heating performance because of its inherent construction. This is because the heat source for heating the passenger room is limited to only a heat energy collected by the inside evaporator 117 from the air in the duct 113 and another heat energy produced when the compressor 103 operates. That is, in the system 110, quick heating of the passenger room is not expected particularly at the warm-up time of the vehicle.